<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    /* 清除默认样式 */
    * {
      margin: 0;
      padding: 0;
    }
    ul,ol {
      list-style: none;
    }
    .lunbo {
      position: relative;
      width: 880px;
      height: 550px;
      border: 1px solid #333;
      margin: 20px auto;
    }
    .lunbo .pic li {
      position: absolute;
      left: 0;
      top: 0;
      width: 880px;
      height: 550px;
      display: none;
    }
    .lunbo .pic .current {
      display: block;
    }
    /* 按钮 */
    .lunbo .btn a {
      position: absolute;
      top: 50%;
      width: 40px;
      height: 40px;
      margin-top: -20px;
      background-color: rgba(255,255,255,0.3);
      font: 20px/40px "宋体";
      text-align: center;
      color: #fff;
      text-decoration: none;
      font-weight: bold;
    }
    .lunbo .btn .leftbtn {
      left: 20px;
    }
    .lunbo .btn .rightbtn {
      right: 20px;
    }
    .lunbo .btn a:hover {
      background-color: rgba(255,255,255,0.6);
    }
    /* 下标 */
    .lunbo .sub { 
      position: absolute;
      left: 40%;
      bottom: 50px;
      width: 240px;
    }
    .lunbo .sub li {
      float: left;
      width: 20px;
      height: 20px;
      margin-right: 20px;
      background-color: rgba(255,255,255,0.4);
      font: 12px/20px "微软雅黑";
      text-align: center;
      color: #666;
      cursor: pointer;
    }
    .lunbo .sub .current {
      background-color: #fff;
    }
  </style>
</head>
<body>
  <!-- 轮播图大结构 -->
  <div class="lunbo" id="lunbo">
    <!-- 图片部分 -->
    <ul class="pic" id="pic">
      <li class="current"><img src="images/lunbo/c1.jpg"></li>
      <li><img src="images/lunbo/c2.jpg"></li>
      <li><img src="images/lunbo/c3.jpg"></li>
      <li><img src="images/lunbo/c4.jpg"></li>
      <li><img src="images/lunbo/c5.jpg"></li>
      <li><img src="images/lunbo/c6.jpg"></li>
    </ul>
    <!-- 按钮 -->
    <div class="btn">
      <a href="javascript:;" class="leftbtn" id="leftbtn">&lt;</a>
      <a href="javascript:;" class="rightbtn" id="rightBtn">&gt;</a>
    </div>
    <!-- 小圆点 -->
    <ol class="sub" id="sub">
      <li class="current">1</li>
      <li>2</li>
      <li>3</li>
      <li>4</li>
      <li>5</li>
      <li>6</li>
    </ol>
  </div>
</body>
<script>
  //全局信号量,存储的是展示的图片的下标
  var idx = 0;

  //1、获取元素
  var lunbo = document.getElementById("lunbo");
  var picUL = document.getElementById("pic");
  var lis = picUL.children;
  var leftBtn = document.getElementById("leftbtn");
  var rightBtn = document.getElementById("rightBtn");
  var ol = document.getElementById("sub");
  var timer;
  var olLis = ol.children;
  //2、右按钮事件，切换到下一张
  rightBtn.onclick = rightHandle;
  //3、左按钮时间，切换到上一张
  leftBtn.onclick = function rightHandle(){
    //信号量增加
    idx -- ;
    if(idx < 0){
      idx = lis.length -1;
    }
    change()
  };
  //4、下标小圆点事件，点哪个小圆点，对应展示相应的图片
  for(var i = 0;i < olLis.length; i++){
    olLis[i].index = i;
    //添加小圆点时间
    olLis[i].onclick = function(){
      idx = this.index;
      change();
    }
  }
  //5、轮播图自动播放效果
  timer = setInterval(rightHandle,2000)
  //6、鼠标移上，停止轮播
  lunbo.onmouseover = function(){ 
    clearInterval(timer);
  }
  //7、鼠标移开，继续轮播
  lunbo.onmouseout = function(){
    timer = setInterval(rightHandle,2000)
  }
  function change(){
     //排他思想
     for(var i = 0; i < lis.length; i++){
      lis[i].className = "";
      olLis[i].className = "";
    }
    lis[idx].className = 'current';
    olLis[idx].className = 'current';
  }

  //右按钮事件
  function rightHandle(){
    //信号量增加
    idx ++ ;
    if(idx >= lis.length){
      idx = 0;
    }
    change()
  }

</script>
</html>